The present invention relates to electric rotating machines and in particular to a method for determining the position of the rotor of a synchronous alternating-current permanent-magnet machine.
As is known, controlling a synchronous alternating-current permanent-magnet machine requires knowing the position of the rotor, which can be determined by means of a suitable sensor installed on the shaft of said machine.
However, when the presence of said sensor is impossible due to cost reasons or other reasons, so-called sensorless algorithms are usually used which, for example by using only current and voltage measurements on the machine, determine the position of the rotor in each instant.
For speeds substantially different from zero, the use of methods based on the counter-electromotive force of the synchronous machine allows good performance, while at speeds close to zero or equal to zero, on isotropic synchronous machines it is not possible to implement so-called sensorless algorithms, since the counter-electromotive force of the motor is nil.
In this case it is possible to use any saturations of the machine, i.e., if the inductance of the machine is a function of the position of the rotor it is possible to use an algorithm of the sensorless type, but in this case it is incorrect to define such a machine as isotropic.
Anisotropic synchronous machines, when supplied by impressed-voltage inverters, due to the variability of the inductance according to the angle of the rotor, impart an information content to the currents of the motor which is independent of rotor speed and allows to deduce the position of the rotor at each instant over time.
However, obtaining information on the position of the rotor from the current of the motor can be extremely difficult. The literature provides many methods, some of which are highly elaborate and difficult to implement, to the point that they cannot be applied to ordinary hardware platforms used for motor control applications, which do not have large computational resources.
As an alternative, if instead of using mathematical algorithms one uses so-called pre-calculated or pre-measured look-up tables of machine inductances as a function of the position of the rotor of said machine (synchronous inductances), said tables must be compiled with extreme accuracy, and this in turn is a significant disadvantage, since extremely accurate tables are also very large and therefore occupy considerable memory on the processor. On the other hand, the advantage of these methods is that they allow to obviate the problem of determining the angle 2xcex8, since it is possible to provide directly the angle xcex8.
The aim of the present invention is to provide a method for determining the position of the rotor of a synchronous alternating-current permanent-magnet machine, which allows to determine the position of the rotor with calculations that are simplified with respect to known types of method and therefore with reduced computational resources.
Within the scope of this aim, an object of the present invention is to provide a method for determining the position of the rotor of a synchronous alternating-current permanent-magnet machine that allows to determine the sin(2xcex8) and cos(2xcex8) parameters with xcex8 as the electrical angle.
Another object of the present invention is to provide a method for determining the position of the rotor of a synchronous alternating-current permanent-magnet machine that allows to obtain from sin(2xcex8) and cos(2xcex8) the pair sin(xcex8) and cos(xcex8) that allows to univocally identify the position of the rotor of the machine.
Another object of the present invention is to provide a method for determining the position of the rotor of a synchronous alternating-current permanent-magnet machine that is highly reliable, relatively simple to provide and at competitive costs.
This aim is achieved at least in part, by a method for determining the position of the rotor of a synchronous alternating-current permanent-magnet machine, which includes, among other features injecting a high-frequency voltage into the machine superimposed on the voltage delivered by the machine control system; measuring the current of the motor and extracting a current that is linked to the injected voltage; and obtaining from said injected voltage and from said corresponding current the electrical angle xcex8 suitable to identify the position of the rotor.
Further characteristics and advantages of the invention will become better apparent from the detailed description of preferred embodiments according to the present disclosure.